Diabetic keratopathy is a complication of diabetes and a major cause of vision loss. There are no effective drugs that can prevent or reverse corneal defects related to diabetes. Two independent longitudinal clinical studies have shown robust therapeutic effects of fenofibrate, a specific agonist of Peroxisome Proliferator-Activated Receptor-? (PPAR?), on diabetic retinopathy. Our preliminary studies using diabetic human donor corneas and animal models suggest a role of PPAR? in maintaining corneal nerve integrity. In our preliminary studies, we have fabricated an innervated 3D in vitro human corneal model that demonstrates basic anatomical and physiological similarities to the corneal tissue in vivo. Using this novel model we began unravelling PPAR??s role in diabetic keratopathy. Significant downregulation of PPAR? expression was seen in cells from both T1DM and T2DM human donors, in agreement with decreased PPAR? levels as shown in diabetic human corneas. Our in vivo preliminary studies have shown that non-diabetic PPAR? knockout (PPAR?-/-) mice have decreased densities of the sub-basal nerve fibers and reduced corneal sensitivity, similar to what is seen in diabetic humans. Furthermore, to our surprise, aged, non-diabetic PPAR? knockout mice naturally developed more severe corneal ulcerations compared to that in age-matched WT mice. Treatment of diabetic rats with fenofibric acid, an active metabolite of fenofibrate, alleviates corneal nerve degeneration in diabetic rats. As shown by Seahorse analysis, mitochondrial function is impaired in PPAR?-/- retina. Based on these preliminary studies, we hypothesize that diabetes-induced down-regulation of PPAR? expression plays a key pathological role in diabetic keratopathy and represents a novel drug target. We propose the following studies to address the hypothesis. First, we will induce diabetes in PPAR?-/- mice and PPAR? transgenic mice over-expressing PPAR? in the cornea, to determine if PPAR? KO exacerbates while PPAR? over-expression alleviates diabetes-induced decreases of corneal nerve density and sensitivity. We will also treat diabetic mice with fenofibrate to determine if activation of PPAR? arrests progression of corneal nerve fiber degeneration. Second, we will determine if the neuroprotective effect of PPAR? is through attenuation of oxidative stress and inflammation, protection of mitochondrial functions and up-regulation of neurotrophic factors using PPAR?-/- mice and PPAR? transgenic mice as well as the innervated in vitro 3D human corneal model. Third, to translate the neuroprotective PPAR? function into a therapy, we will evaluate therapeutic efficacy of topical application of a proprietary fenofibrate eyedrop on diabetes-induced nerve fiber degeneration. This study has potential to identify a new function of PPAR? in the cornea. These studies have potential to establish a novel pathogenic mechanism for diabetic keratopathy and to lead to the development of a novel therapy.